In order to improve a machining precision, the good characteristics in regarding to the vibration, the noise, etc. are required of the bearing for the machine tool spindle. Also, the grease lubrication that is easy to handle and is effective in an environmental aspect and a cost aspect is required of the bearing for the machine tool spindle to attain a high-speed running performance and a long lifetime.
It is normal that the grease-lubricated rolling bearing for use in the machine tool spindle is lubricated merely with the initially sealed grease not to generate a heat. When the bearing is run at a high speed in the initial stage of the grease filling without the running-in trial of the grease, an abnormal heat generation is caused owing to the jamming or the churning resistance of the grease. Therefore, the grease is brought into its optimum state by executing the running-in trial for several hours.
Recently, the running speed of the machine tool spindle is increased more and more. It is not unusual for the bearing for bearing the spindle to be used in the environment of dmN (=(bearing bore diameter+bearing outside diameter)÷2×rotation speed (rpm)) one million or more. The grease-lubricated rolling bearing tends to have a short lifetime in the high-speed running rather than the rolling bearing that is lubricated with the oil such as the oil air, the oil mist, or the like. In the case of the grease lubrication, the bearing is seized up by the grease degradation prior to the end of the rolling contact fatigue life of the bearing. In the case where the number of revolution is extremely high, the seizure of the bearing is caused in an early stage because the grease is degraded in a short time or the formation of the oil film is insufficient.
For this reason, in order to achieve an enhanced lifetime of the bearing, the method of forming concave portions in the inner ring of the bearing, then storing previously the grease in these concave portions, and then supplying the stored grease to the bearing has been proposed (for example, see JP-A-1-67331, JP-A-4-132220, and JP-A-6-35659).
Also, in order to achieve an enhanced lifetime of the bearing, the method of forming concave portions in the spindle into which the bearing is fitted, then storing previously the grease in these concave portions, and then supplying the grease stored in the concave portions to the bearing has been proposed (for example, see JP-A-6-35653).
Also, in order to overcome such problem, in JP-A-2003-113846, the applicant of this application has proposed the grease-lubricated rolling bearing in which the supply hole is provided in the outer ring and then the grease is supplied via the supply hole in such a manner that a supply amount of grease is set to 0.1 to 4% of a bearing space volume. According to this rolling bearing, the abnormal temperature rise of the bearing can be suppressed in running and thus the generation of the seizure of the bearing can be prevented. Therefore, according to the rolling bearing set forth in JP-A-2003-113846, execution of the running-in trial is not needed because the abnormal temperature rise can be avoided.
In this case, the rolling bearing set forth in JP-A-2003-113846 can be constructed not to generate the abnormal temperature rise by supplying the grease in such a way that a supply amount of grease is set to 0.1 to 4% of the bearing space volume. However, a supply amount of grease is set largely, it is possible that a temperature pulsation is generated.
The evaluation test was made to estimate this temperature pulsation. In the angular contact ball bearing having the bore diameter of 65 mm, it was found that, if the grease in excess of 1% of the bearing space volume (1% of the bearing space volume corresponds to 0.15 cc) is fed with one shot, the temperature pulsation of about 1° C. to 2° C. is generated in an instant when the grease is supplied.
This temperature pulsation does not matter in the normal application that does not demand a precision. However, in the rolling bearing used in the spindle of the machine such as the machine tool oriented toward the mold application, or the like that demands strictly a precision, there is a possibility that the temperature pulsation changes a length of the spindle to exert an influence upon a machining precision.
Also, in order to prevent the excessive feed of the grease during the grease supply, the grease feeding unit for supplying the additional grease only when the abnormality of the bearing is sensed has been proposed (see JP-A-63-53397 and Japanese Patent No. 3167034).
In this case, since the above unit supplies the additional grease after the abnormality was generated in the bearing, it is possible that the bearing has already been damaged at a point of time when the additional grease is supplied. The damage of the bearing causes a reduction in a run-out precision of the machine tool, and thus the machining precision of the machine tool is lowered. Therefore, in order not to cause even slight damage due to the lubrication failure, the normal grease supply system supplies the grease at a predetermined supply interval based on the severest conditions in the environment in which the bearing is used.
However, in the case where the supply system is set to supply the grease at a predetermined supply interval based on the severest conditions in the environment in which the bearing is used, such supply system supplies the excessive grease to the inside of the bearing even when the bearing using conditions are not so severe. Thus, there exists such a problem that the grease is filled excessively in the bearing.
For example, according to the experiment performed by the applicant, when the spindle of 65 mm diameter supported by the bearing is rotated at a rotation speed 22000 min−1 without the grease feeding, degradation of the grease was caused in 100 hours and thus the bearing was damaged whereas, when the same spindle is rotated at a rotation speed 18000 min−1 without the grease feeding, the bearing was damaged in 1000 hours that is ten times the above case. As a result, the grease supply executed every predetermined interval is ineffective when the using conditions are not severe, which results in a wasteful increase in the supply number of times. In addition, the grease supplied excessively in response to the increase in the supply number of times makes a bearing temperature unstable.
Also, in the above setting, the grease is supplied irrespective of the operating conditions of the bearing. Thus, the grease is also supplied steadily into the bearing that is stopped. Therefore, when the stopped bearing is operated again, the churning resistance of the grease is increased by the added grease and thus a sudden temperature rise is caused.
In addition, as the system for monitoring the discharge condition of the lubricating oil in the lubricating system, systems described in the following are known.
1. The system that stores the lubricating oil in a tank (pump) in the lubricating system, and then monitoring whether or not a pressure of the lubricating oil is within an available pressure range of the lubricating system connected to the valve, by sensing the pressure of the lubricating oil discharged into the valve (fixed-displacement piston pump) (see JP-A-2003-113846).
2. The system that monitors whether or not the lubricating oil is discharged, by sensing a motion of a piston in the mechanical fixed-displacement piston pump (see JP-A-5-87293).
3. The system that heats a part of the lubricating oil that is discharged from the mechanical fixed-displacement piston pump into the piping, and then monitoring the discharge condition of the lubricating oil by sensing a flow of the heated lubricating oil (see JP-UM-B-6-29742).
4. The system that monitors the discharge condition of the grease by sensing a temperature generated when the grease is supplied to the bearing unit (see JP-A-11-270789).
As shown in FIG. 113, in a grease supply system 1640, an air is supplied to a mechanical fixed-displacement piston pump 1642 when a valve (solenoid valve) 1641 is turned ON, and then a fixed displacement piston 1642a is operated to discharge a grease Gr into a piping 1644 that supplies the grease to a bearing 1643. Then, the grease is supplied to the bearing unit in the spindle. Also, when the valve (solenoid valve) 1641 is opened, the air is supplied into a grease tank 1645 to apply a pressure to an in-tank piston 1646.
The air is not supplied to the mechanical fixed-displacement piston pump 1642 when the valve (solenoid valve) 1641 is turned OFF, and then the fixed displacement piston 1642a returns to its home position. At this time, the air used to apply the pressure to the piston in the grease tank is not released because of the presence of a resistance body 1649 provided to the grease tank, so that the grease Gr in the grease tank 1645 is supplied into the mechanical fixed-displacement piston pump 1642.
A minute amount of grease can be supplied intermittently into the bearing unit in a fixed quantity by repeating above operations.
However, when the grease is exhausted in the grease tank that stores the grease to be supplied to the mechanical fixed-displacement piston pump, the grease is not supplied from the mechanical fixed-displacement piston pump. Thus the lubrication failure is generated in the bearing and then the bearing is seized up.
Also, in the case where, when the piston of the mechanical fixed-displacement piston pump is returned, no pressure is applied to the grease in the grease tank because the solenoid valve is turned OFF to feed the grease to the mechanical fixed-displacement piston pump, the grease is not supplied from the grease tank to the mechanical fixed-displacement piston pump. Thus, the grease is not discharged from the mechanical fixed-displacement piston pump. Therefore, there was such a problem that the lubrication failure is generated in the bearing and then the bearing is seized up.
Also, as the grease supply system for use in the general industry, a grease supply system 1650 shown in FIG. 114 gives a resistance-type pneumatically-operated pump type system that supplies the grease by using an external energy given from an external air supply source.
In the grease supply system 1650, the air supply source is connected to one end portion of a grease tank 1651 to communicate with the same and also a grease supply piping 1652 is connected to the other end portion of the grease tank 1651 to communicate with the same. A base end portion of the grease supply piping 1652 is communicated with a discharge port 1653, and a nozzle 1654 is provided to a top end portion of the grease supply piping. The nozzle 1654 is arranged on the side portion of a bearing unit 1655 into which the ball bearing, the cylindrical roller bearing, or the like is installed.
In such grease supply system 1650, when a pressure is applied to a piston 1656 in the grease tank 1651 for a predetermined time, a grease 1657 reserved in the grease tank 1651 is fed to the nozzle 1654 through the discharge port 1653 and the grease supply piping 1652 and then is discharged into a bearing space of the bearing unit 1655 from the nozzle 1654 (for example, see Sanei Tech Inc. “EFD liquid chemical discharge system catalog” (page 4 to page 17)).
As still another configuration of the grease supply system, a grease supply system 1660 shown in FIG. 115 has the similar configuration to that of the grease supply system 1650 shown in FIG. 114, and gives a resistance-type pneumatically-operated pump type system that supplies the grease by using an external energy given from an external air supply source.
In the grease supply system 1660, the air supply source is connected to one end portion of a grease tank 1661 to communicate with the same and also a grease supply piping 1662 is connected to the other end portion of the grease tank 1661 to communicate with the same. A base end portion of the grease supply piping 1662 is communicated with a discharge port 1663 of the grease tank 1661, and a top end portion is connected to a grease supply hole 1667, which is formed in the radial direction of an outer ring 1666 in a bearing unit 1665 into which the ball bearing, the cylindrical roller bearing, or the like is installed, to communicate with the same.
In such grease supply system 1660, when a pressure is applied to a piston 1668 in the grease tank 1661 for a predetermined time, a grease 1669 reserved in the grease tank 1661 is fed through the discharge port 1663, the grease supply piping 1662, and the grease supply hole 1667 and then is discharged into a bearing space of the bearing unit 1665 from the outside diameter portion of the outer ring through the grease supply hole 1667 (for example, see Sanei Tech Inc. “EFD liquid chemical discharge system catalog” (page 4 to page 17)).
As yet still another configuration of the grease supply system, a grease supply system 1670 shown in FIG. 116 gives a mechanically-operated pump type system that supplies the grease by using an external energy generated by a prime mover such as a motor, or the like.
In the grease supply system 1670, a motor 1672 is installed into a grease tank 1671 and an external thread 1673 is provided on an output shaft of the motor 1672. Then, an internal thread 1675 of a piston 1674 is screwed on the external thread 1673 of the output shaft.
A grease supply piping 1676 is connected to an end portion of the grease tank 1671 to communicate with the same, and also a base end portion of the grease supply piping 1676 is communicated with a discharge port 1677 of the grease tank 1671. A nozzle 1678 is provided to a top end portion of the grease supply piping. The nozzle 1678 is arranged on the side portion of a bearing unit 1679 into which the ball bearing, the cylindrical roller bearing, or the like is installed.
In such grease supply system 1670, the output shaft of the motor is turned when an electric current is supplied to the motor 1672, then the piston 1674 is moved forward in the grease tank 1671 by the turning of the output shaft, and then a pressure is applied to a grease 1680 in the grease tank 1671. Then, the grease 1680 is fed to the nozzle 1678 through the discharge port 1677 and the grease supply piping 1676, and then is discharged into a bearing space of the bearing unit 1679 from the nozzle 1678. If the grease supply piping 1676 is connected to the grease supply hole, which is formed in the bearing unit 1679 in the diameter direction of the outer ring, in the same manner as shown in FIG. 115 to communicate with the same, in some cases the grease 1680 is discharged from the outside diameter portion of the outer ring into the bearing space (for example, see the ING Corporation “Automatic Continuous Grease Feeder made in Germany” perma (page 2 to page 4)).
However, in the grease supply systems 1650, 1660, 1670, a discharge quantity of grease is largely varied according to the conditions such as an inner diameter and a length of the piping extended from the grease pressurizing portion to the bearing, a shape of the nozzle, a temperature, etc. Therefore, a time required to apply a pressure to the grease must be controlled/adjusted every time when these conditions are changed. As a result, there existed the problem that it is difficult to execute the stable discharge of the grease.
Also, in the grease supply system 1670, a residual pressure still remains for a long time in the grease remained in the piping from the grease pressurizing portion to the bearing, and thus such grease tends to flow though an mount of the grease is minute. Therefore, the flow of the grease is different between the inner diameter portion and its neighborhood and the center portion and its neighborhood in the piping. Also, if the grease is kept in such condition for a long time, component separation of the grease is caused and thus the greases having a different consistency respectively are present in the piping. As a result, there existed the problem that it is impossible to discharge the grease in a fixed quantity.
Also, in the grease supply system 1670, depending on the shape of the grease supply piping 1676 on the latter part of the discharge port 1677, the grease 1680 is not discharged because of the resistance in the pipe even though the piston 1674 is operated. Thus, it is likely that the grease tank 1671 should be expanded by the pressure.
In addition, in JP-A-2000-288870, the technology to manage the contamination such that the extraneous material such as dust, liquid, or the like does not enter into the bearing portion of the spindle unit is set forth. However, there is a limit to the lifetime of the grease even if such management is applied, and thus the long lifetime similar to that obtained when the oil air lubrication or the oil mist lubrication is applied cannot be obtained.
Also, according to the technology in JP-A-2003-113846 that the applicant of this application has already proposed, the lifetime of the grease is prolonged, nevertheless the temperature rise of the outer ring becomes 70 to 80° C. at a dmN 1,800,000 level when no cooling is applied. Thus, it is possible that the seizure of the bearing is brought about due to the oxidative degradation of the grease or the defective formation of the oil film.
In the grease for the high-speed running, the base oil having a viscosity equivalent to VG22 is often used to suppress the heat generation. In the high-speed running, Isoflex NBU15 manufactured by NOK Crewbar Inc. is normally used for the machine tool spindle. This grease has a base oil viscosity of 20 mm2/s (40° C.). When a bearing temperature becomes 70 to 80° C., a kinetic viscosity of the base oil is 6 to 8 mm2/s and thus it is difficult to keep the oil film.
Also, in the spindle unit of the machine tool, if the cutting fluid enters into the bearing in the spindle unit from the outside, a lubricating performance of the spindle bearing is deteriorated to cause the seizure of the bearing. Therefore, the labyrinth seal shown in FIG. 117 or the air seal is arranged as the cutting fluid entering preventing means in the cutting fluid entering area extended from a clearance between the spindle and the front end of the housing to the bearing (for example, see JP-UM-A-4-90770, JP-A-2002-239867).
However, these cutting fluid entering preventing means cannot completely prevent the entering of the cutting fluid.
Therefore, as shown in FIG. 118, the bearing for sensing the cutting fluid entering into the bearing by providing a cutting fluid sensor to the bearing has been provided (for example, see JP-A-2002-206528).
However, in JP-UM-A-4-90770, there existed the problem that the cutting fluid enters into the inside of the spindle unit. Also, in JP-A-2002-239867, according to the method of exhausting the extraneous matter from the drain hole by the rotation of the spindle, there existed the problem that the exhausting capability is lowered when the rotation speed is slow. In addition, in JP-A-2002-206528, according to the method of sensing the entering of the cutting fluid by the sensor provided to the inside of the bearing, the cutting fluid is sensed after the cutting fluid has already entered into the inside of the bearing. Thus, there existed the problem that either the seizure of the bearing occurs or the maintenance such as exchange, decomposition/rinsing, etc. of the bearing is needed. In particular, many instances were found in the grease lubrication where the grease that was sealed once is rinsed out by the cutting fluid when the cutting fluid enters into the bearing and thus the bearing is damaged.
Further, as shown in FIG. 119, a bearing unit 1701 is proposed in which exhausted lubricant storage spaces 1712 used to exhaust the lubricant on the inside of the bearing to the outside of the bearing are formed in an outer ring spacer 1711.
This bearing unit 1701 is constructed such that the lubricant reserved in the exhaust spaces 1714, 1712 can be sucked periodically.
In this case, a reference numeral 1715 denotes a grease supply hole, 1716 a housing, 1717 an inner ring spacer, 1718 a ball, 1719 an outer ring, and 1720 an inner ring.
Also, a bearing unit 1702 shown in FIG. 120 is constructed in such a fashion that a sealing member 1721 is fitted onto one side of a bearing 1713 and also the lubricant flows to a wider space 1722 on the opposite side to the sealing member 1721. Here, a reference numeral 1723 denotes an outer ring spacer.
However, since the above bearing unit 1701, 1702 (see FIG. 119 and FIG. 120) is constructed to push out the lubricant to the outside of the bearing unit 1701, 1702 by supplying further the lubricant into the bearing space that has already been filled with the lubricant by the continuous supply, a force of exhausting the lubricant to the outside of the bearing is small.
Therefore, the storage spaces 1712 formed in the outer ring spacer 1711 cannot be filled with the exhausted lubricant. As a result, there existed the problem that it is difficult to continue to supply the lubricant for a long time.
Besides, there also existed the problem that, when the exhaust of the lubricant to the outside of the bearing unit 1701, 1702 is performed by the suction applied from the outside of the bearing unit, it is difficult to remove completely the lubricant in the bearing unit 1701, 1702.
Also, as shown in FIG. 121, a method of supplying the grease to a bearing 1752, in which an outer ring 1753 is fitted into a housing 1751, from the outside may be considered.
By way of example, a bearing grease supply system 1750 in which a grease filling hole 1754 is passed through the housing 1751 and a supply hole 1755 is passed through the outer ring 1753 to align with the grease filling hole 1754 is known.
According to the bearing grease supply system 1750, since the grease supply system (not shown) is connected to the grease filling hole 1754 via the grease supply piping, the grease can be filled into the bearing 1752 from the grease supply system via the grease supply piping, the grease filling hole 1754, and the supply hole 1755. In this case, according to the above configuration, since a positional alignment between the supply hole 1755 and the grease filling hole 1754 is needed, it takes much time and labor to incorporate the bearing into the housing.
For this reason, such a configuration may be employed that the supply hole, which supplies the grease into the bearing, may be formed in the outer ring and also either the annular groove containing the supply hole may be formed on the outer periphery of the outer ring or the annular groove facing to the supply hole may be formed on the inner periphery of the housing, so that a positional alignment between the housing and the bearing in assembling may be eliminated. In the case of the above configuration, in order to supply the grease being supplied from the grease filling hole in the housing from the outer ring supply hole to the inside of the bearing via the annular groove, following three respects are important.
(i) A relationship between a cross section of the annular groove and a peripheral length of the cross section of the annular groove.
(ii) A value of a clearance between the housing and the bearing outer ring.
(iii) A length of an outer surface, which contacts the housing in the axial direction, of the bearing outer ring except the annular groove.
When a value of (i) is small, the grease acts as a resistance when such grease passes through the annular groove. Therefore, the grease does not reach the supply hole in the outer ring and thus the grease cannot be supplied to the inside of the bearing.
When a value of (ii) is large, the grease flowing through the annular groove leaks from the clearance between the housing and the bearing outer ring and then is exhausted to the outside of the bearing. Therefore, the grease is not supplied from the supply hole in the outer ring to the inside of the bearing.
When a value of (iii) is small, the grease flowing through the annular groove leaks from the clearance between the housing and the bearing outer ring and then is exhausted to the outside of the bearing. Therefore, the grease is not supplied from the supply hole in the outer ring to the inside of the bearing.
The present invention has been made in view of the above circumstances, it is an object of the present invention to provide a rolling bearing capable of running at a high speed and enhancing a lifetime of the bearing by supplying a grease, a grease supply system, a spindle unit, a grease supply method, and a grease supply program.
In particular, the present invention provides a rolling bearing, a grease supply system, a spindle unit, a grease supply method, and a grease supply program, which are capable of suppressing a temperature pulsation upon supplying the grease, lessening the workload of the operator because the fitting operation of the bearing can be completed in a short time, and executing a quantitative supply to discharge the grease intermittently in a minute and predetermined quantity without the influence of the piping.
Also, it is another object of the present invention to provide a spindle unit capable of sensing an entering of a cutting fluid into the inside of the spindle unit before the cutting fluid enters into the inside of the bearing, and thus capable of maintaining stably the lubricating performance of the spindle bearing for a long time not to stop the running of the machine for a long time.
In addition, it is still another object of the present invention to provide a spindle unit capable of exhausting the supplied lubricant continuously and executing stably the continuous running for a long time, and capable of exhausting the lubricant to the outside of the spindle unit without fail and keeping the good lubricated condition by executing the lubricant supply that makes easy and stable maintenance possible, and in turn capable of attaining an enhanced lifetime of the bearing.